1. Field of the Invention
The present invention relates to substantially dry, viable bacterial compositions, nutritional supplements containing such compositions, and methods of stabilizing dried viable bacteria.
2. Background
Living bacteria may provide a variety-of nutritional benefits in humans and animals. In particular, bacteria of the genus Lactobacilli are one of the major groups of intestinal and fecal organisms found in humans and animals that are understood to confer certain health benefits to humans and animals. The significant health and nutritional benefits of Lactobacilli, and in particular the strain Lactobacillus acidophilus, are well known. [See, e.g., Speck, M. L and Katz, "R. L., "ACDPI Status Paper: Nutritive and Health Values of Cultured Dairy Foods," Cult. Dairy Prod. J., 15(10):4 (1980)]. Lactobacilli found in the human intestinal tract include Lactobacillus acidophilus, Lactobacillus plantatum, and Lactobacillus cellobiosus.
The nutritional benefits of Lactobacilli are manyfold. This genus of bacteria are known to improve the nutritional value of foods by increasing the quantity as well as the availability, digestibility, and assimilability of nutrients. This is accomplished by the fermentation by Lactobacilli of foods, such as proteins, fats, or carbohydrates, that results in the predigestion such foods--in other words, predigestion by Lactobacilli renders the proteins, fats, and carbohydrates in a form that is more readily absorbed and digested in mammals. [Friend, B., Shahani, K., J. Applied Nutrition, 36:2 (1984)]. As a result, the nutrients demonstrate an effective increase in their ability to be utilized by the body.
One such compound that Lactobacilli are known to predigest is lactose. Many humans are lactose intolerant--i.e., unable to metabolize lactose (milk sugar)--due to the lack of the .beta.-galactosidase (also known as lactase) enzyme that metabolizes milk sugars. Persons lacking this enzyme may suffer from severe gastrointestinal problems if lactose-containing products are consumed. This nutritional problem may be overcome by Lactobacillus acidophilus fermentation since this bacterial species produces .beta.-galactosidase which metabolizes a significant portion of the lactose from the ingested dairy product, thereby preventing gastric complications resulting from its ingestion. [Kilara, A., Shahani, K., J. Dairy Sci., 61:2031 (1976)].
Lactobacilli are also understood to be involved in the synthesis of vitamins. Specifically, depending on the conditions of the bacterial culture, the fermentation of Lactobacilli have been reported to synthesize folic acid, niacin, vitamin B.sub.12, and vitamin B.sub.6. [Friend and Shahani, cited above]. Lactobacilli are also understood to destroy certain anti-nutritional compounds. Certain protein sources, such as raw soybeans, possess anti-nutritional factors such as trypsin-inhibitor, phytate or flatulena. Fermentation of soy by Lactobacilli is understood to reduce or eliminate these factors. [Friend and Shahani, cited above].
Dietary supplementation with Lactobacillus acidophilus has been demonstrated as a viable treatment for certain conditions of the intestinal tract including antibiotic-induced imbalances in gastrointestinal microflora, hypercholesterolemia, E. coli infection, chronic granulomatous disease, and lactose indigestion. [See, e.q., Shauss, "Method of Action, Clinical Application, and Toxicity Data," J. Advancement Med., 3:163 (1990)]. In addition, Lactobacilli synthesize several antimicrobial substances including lactic acid, acetic acid, benzoic acid, and hydrogen peroxide. [Friend and Shahani, cited above]. By aiding in the predigestion of certain foods, dietary supplementation with Lactobacilli cultures may aid in preventing the over-proliferation of cells. More specifically, diets high in animal fat, protein or fried foods appear to increase the risks of certain kinds of cancers, such as colon and breast cancers. By aiding in the predigestion of fats and proteins, Lactobacilli may be implicated in the inhibition the chemical procarcinogens present in the gastrointestinal tract that result from the digestion of these kinds of foods. [Friend and Shahani, cited above].
Lactobacilli plays important roles in food preservation, since its use is known to assure preservation of highly perishable foods, especially where refrigeration is lacking. The food preservation activity of the compositions of the present invention results from the inclusion of live, stable bacteria that can flourish in the foodstuffs and thereby prevent the overgrowth of other bacteria that may adversely affect the food.
3. Prior Art
Nutritional supplementation of the human diet by orally administered cultured bacterial cultures, including Lactobacillus acidophilus preparations, is known. The main problem associated with the use of bacterial cultures in dietary supplementation is the finite shelf-life of live bacteria , i.e., the bacteria will expire after a certain period of time when in dried form and in non-refrigerated storage. Although methods to increase the shelf-life of bacteria used to supplement the diet of humans and animals are known, none has succeeded in maintaining bacterial counts at levels substantially approximating their initial levels after about 180 days, and none are known to actually increase bacterial counts over that time. Moreover, inorganic compounds, such as silicon dioxide polymeric materials, have been proposed to stabilize dried bacterial cultures, [See, e.g., De Silva et al., "Lactic Acid Bacteria on Anhydrous Silica Gel for Three Years," J. of Food Protection, 46:699-701 (1983)]. However, such methods are inadequate to sufficiently stabilize bacteria over a period of more than about 180 days. In other words, the efficacy of such nutritional supplements is reduced due to the inherent instability of live Lactobacillus acidophilus cultures. Over time, such cultures die and are thus less effective.
For example, U.S. Pat. No. 5,531,988 describes a nutritional composition comprising Lactobacillus acidophilus and concentrated immunologically active immunoglobins capable of binding and inactivating antigens that are detrimental to gastrointestinal health. This patent, however, provides no evidence of enhanced viability of the bacteria cultures beyond a period of a few days. In addition, U.S. Pat. No. 5,501,857 describes an oral nutritional supplement for livestock which includes "incompatible" live microbial cultures, such as Lactobacillus acidophilus, in combination with, but necessarily physically separated from, a vitamin and mineral composition. As described in this patent, the incompatible ingredients would deleteriously react if combined with one another. Although this patent describes an enhanced shelf-life of the bacteria resulting from the separation of the vitamin and mineral ingredients from the Lactobacillus acidophilus culture, the viability of the bacteria shows a significant decrease over a period of a few months.
Other solid compositions comprising Lactobacillus acidophilus have been taught. Various compositions comprising combinations of bacteria with selected carriers are said to aid in increasing the shelf-life of dried bacteria. See, e.g., U.S. Pat. Nos. 3,677,898, 3,898,132, 4,229,544, 4,205,132, 4,518,696, 4,115,199, 3,616,236, and 1,957,555, each of which describe methods to treat dried bacterial compositions in order to increase the shelf-life. Each of the methods disclosed in these patents, however, results in a substantial decrease in bacterial counts over a period of about 180 days or greater. U.S. Pat. No. 4,956,295 is exemplary of efforts to increase the stability of dried bacterial cultures and provides perhaps the best example of the current advances in this field. This patent discloses dried bacterial compositions that combine silicon dioxide particle carrier with mixtures of inorganic salts to increase the shelf-life of the bacteria. However, as is evident from this patent, the shelf-life of Lactobacillus acidophilus bacteria exhibited nearly a 100 fold decrease in bacterial counts over a 180 day period. In addition, other bacterial cultures demonstrated a significant decrease in bacterial counts in spite of the disclosed method.
Hence, there remains a need in the art for compositions of solid, dry bacterial cultures, including Lactobacillus acidophilus cultures, that are stable for long periods of time under ambient conditions and which are suitable for ingestion by humans and animals.